~ Musings on weather and science

The forecast has gotten very simple for the next week. A strong flat ridge of high pressure and British Columbia low pressure centers will combine to give us a very dry and stable pattern across the west for the next week. High temperatures will be in the low to mid-90s throughout the next week, and the skies will stay mostly blue, although with all that heat a few afternoon cumulus clouds are not out of the realm of possibility.

Yesterday I mentioned that every so often the earth’s magnetic field reverses. There’s no real clear reason why the flipping occurs, although several theories have been proposed, all of which are hard to prove. And although the flipping seems to occur almost instantly from a geological perspective, it probably takes anywhere from a hundred to a few thousand years to complete. The last one happened 780,000 years ago… or “Pre-Geologists.”

Just how do we know that? We can thank molten lava. Basalts on the ocean floor, for example, contain a mineral called magnetite which, as its name implies, is magnetic. Analysis of sea floor basalts show alternating bands of north and south oriented magnetite crystals, showing the earth’s magnetic field made similar flips as the sea floor was extruded.

But those same measurements were used to finally prove what was once a very controversial theory: Plate Tectonics.

In the 50s and 60s, electronic magnetometers were used to survey the ocean floor. What they discovered turned the geologic world on its head. They found a very consistent “striping” of normal and reversed magnetic polarity in the sea floor rocks. These stripes occurred in parallel bands radiating out from a long north-south running undersea ridge. What this showed was the seafloor was being created in what is now known to be a “spreading center.” Magma came to the surface along that underwater ridge, and solidified, spreading out in both directions, proving that plate tectonics (moving of continental plates) was indeed occurring. During times of normal magnetic polarity, the rocks being created stayed normal. If they were created during times of reverse polarity, the rocks would freeze that magnetic orientation in place. It was quite a revelation, and changed the face of geologic thought. It can even be used to calculate just how fast the plates are sliding around on to of the earth’s mantle.